1. Field of the Invention
The present invention relates in general to a pipe having a flange mounted thereon, and more particularly to a flanged pipe unit which is connected to a certain device by using the flange mounted thereon. More specifically, the present invention is concerned with a flanged pipe unit which is widely used for piping the cooling system of an automotive air conditioner.
2. Description of the Prior Art
In the cooling system of an automotive air conditioner, many devices are connected through pipes in which a refrigerant flows. For connecting the pipes to the devices, various measures have been proposed and put into practical use.
One of them is shown schematically in FIG. 3 of the accompanying drawings. In this measure, a flanged pipe unit 50 is used. That is, a flange 1 tightly disposed on a pipe 5 is used for connecting the pipe 5 to a device 7. That is, a leading pipe portion projected from the unit 5 is put into a bore 8 of the device 7, and then the flange 1 on the pipe 5 is secured to the device 7 by means of bolts (not shown). Denoted by numerals 6 and 9 are aligned bolt holes formed in the flange 1 and the device, with which one bolt is incorporated. Although not shown in the drawing, the blind hole 9 has a threaded inner wall with which a threaded leading end of the bolt is engaged.
The tight mounting of the flange 1 on the pipe 5 is carried out by using the following technique.
First, a flange 1 is prepared, which has a through bore 2 including a larger diameter portion 3 and a smaller diameter portion 4 between which a slanted intermediate portion 1c is defined. Then, a pipe 5 is prepared, which has therethroughout an outer diameter slightly smaller than the diameter of the smaller diameter portion 4 of the flange 1. Then, the pipe 5 is inserted into the through bore 2 of the flange 1 having a leading end portion thereof projected from an inner surface 1a of the flange 1. The inner surface 1a is the surface at which the larger diameter portion 3 of the through bore 2 terminates. Then, with the pipe 5 and the flange 1 kept held by a holding tool (not shown), the projected leading end portion of the pipe 5 is punched by a punch 51. With this, the leading end portion of the pipe 5 is radially outwardly expanded in such a manner that a deeper part of the expanded portion is intimately engaged with the inner surfaces of the larger diameter and slanted intermediate portions 3 and 1c of the bore 2, as shown in the drawing. With this, a so-called interlocked connection is achieved between the flange 1 and the pipe 5. After this, the flange 1 is bolted to the device 7 in the above-mentioned manner to effect a hermetically sealed connection between the pipe 5 and the device 7.
However, the above-mentioned technique for the interlocked connection has the following drawbacks.
That is, as is seen in FIG. 3, a certain clearance "C" is inevitably produced between the smaller diameter portion 4 of the bore 2 of the flange 1 and the outer surface of the pipe 5. Such clearance "C" tends to collect water, dust and the like, which causes corrosion of the pipe 5. When the flange 1 is of a cast member, the clearance "C" is much marked because of usage of a two-piece type casting die for casting the flange 1. In fact, each half of this die has a certain draft which causes the smaller diameter portion 4 (also the larger diameter portion 3) to have a tapered inner surface, thereby increasing the size of the clearance "C". Furthermore, the clearance "C" tends to permit vibration of the pipe 5 relative to the fixed flange 1 particularly when the cooling system is in operation. Of course, such vibration is undesired in view of fatigue of the pipe 5 and possibility of cancellation of the interlocked connection between the flange 1 and the pipe 5. Although the clearance "C" may be filled with a packing material, such work increases the cost of the cooling system.